
%% kb() ->
%%     [pls:rule(liked_by, [pls:v('M'), pls:v('N')],
%%               [pls:call(likes, [pls:v('N'), pls:v('M')])]),
%%      pls:fact(likes, [zoa, sarah]),
%%      pls:fact(likes, [robert, sarah]),
%%      pls:fact(likes, [zoa, milk]),
%%      pls:fact(likes, [robert, cheese]),
%%      pls:fact(likes, [robert, zoa]),
%%      pls:fact(likes, [sarah, zoa])
%%     ].


liked_by(M, N) :-
    likes(N, M).


likes(zoa, sarah).
likes(robert, sarah).
likes(zoa, milk).
likes(robert, cheese).
likes(robert, zoa).
likes(sarah, zoa).
